Battery pack and method for preventing uncontrolled charging of batteries in battery pack

Abstract

A battery pack configured to supply power to a common load and including a first battery and a second battery and a method of preventing uncontrolled charging of batteries in the battery pack. The battery protection circuit is configured to prevent uncontrolled charging of the first battery or the second battery due to a voltage difference between the first battery and the second battery.

Description

Technical Field

[0001] The present disclosure generally relates to a battery powerpack connected to a load such as a power tool; in particular, to features for protecting the powerpack from damage due to component failure or uncontrolled charging; and more particularly, to a battery pack and a method for preventing uncontrolled charging of batteries in the battery pack. Background Art

[0002] Portable battery-powered tools can rely on rechargeable battery packs for power. The battery pack can be directly connected to the tool (i.e., inserted into the tool), or can be configured as a self - contained unit (such as a backpack or a body - worn battery pack) that can be carried by the user and electrically tethered to the tool. As the use and convenience of portable tools have grown, the demand for the power density and efficiency of these battery packs has also increased in order to provide greater power and longer run - times for the tools.

[0003] In this regard, the use of lithium - ion (Li - ion) batteries in battery packs has grown, largely due to the increased power density characteristics of these batteries. Multiple lithium - ion batteries can be combined in parallel in the battery pack to further increase the capacity of the battery pack.

[0004] However, a parallel configuration of multiple batteries can lead to potential problems that must be monitored and corrected / prevented. For example, when two batteries are placed in parallel, the voltage difference between the batteries can cause one battery to charge the other. Particularly for lithium - ion batteries, this uncontrolled charging between batteries can lead to poor performance, damage, or even failure of the battery pack.

[0005] It is well - known to use diodes to prevent negative current in a circuit (and protect the battery). However, diodes cause a relatively large voltage drop, thus affecting the power supplied to the tool and therefore potentially having a negative impact on performance. Additionally, without significant heat dissipation, diodes generally cannot handle the high - current, low - voltage power requirements of power tools.

[0006] Using back - to - back MOSFETs connected in series between a lithium - ion battery pack and an output load is a known configuration in conventional battery protection circuits. An integrated circuit (IC) controls the on / off state of the MOSFETs and the charging and discharging modes of the battery. However, if one of the MOSFETs is damaged or short - circuited, this configuration of multiple batteries in parallel is vulnerable to single - point failures and uncontrolled charging of one of the batteries.

[0007] It would be desirable to configure a battery protection circuit for a battery pack having multiple batteries that prohibits battery - to - battery charging and protects the batteries in the event of a component failure causing negative current to flow into one of the batteries. Summary of the Invention

[0008] Aspects and advantages of the present disclosure will be set forth in part in the following description, or may become apparent from the description, or may be learned by practice of the technology.

[0009] According to one embodiment, a battery pack is configured to supply power to a common load, such as a portable power tool. The battery pack includes a first battery and a second battery. An associated battery protection circuit is configured to prevent uncontrolled charging of the first battery or the second battery due to a voltage difference between the first battery and the second battery.

[0010] In a particular embodiment, for each of the first battery and the second battery, the battery protection circuit includes back-to-back MOSFETs connected in series between the respective battery and the common load. A controller connected to the MOSFETs gates the MOSFETs during the power supply mode of the battery pack to prevent the first battery and the second battery from supplying power to the common load in parallel.

[0011] The MOSFETs can be located at the positive high side of each of the first battery and the second battery, or at the negative low side of each of the first battery and the second battery.

[0012] In yet another embodiment, the battery protection circuit can further include a device for detecting a negative current flowing into each of the first battery and the second battery, which negative current can be caused by a fault or short circuit in one of the MOSFETs.

[0013] In one embodiment, the detection device can include a shunt resistor connected in series between the back-to-back MOSFETs of each of the first battery and the second battery and the common load. The battery protection circuit detects the negative current flowing through the shunt resistor and isolates the first battery or the second battery when a negative current above a threshold level is detected through the shunt resistor associated with the respective first battery or second battery.

[0014] The battery protection circuit can include a comparator circuit configured to generate a latch trip signal when one or a combination of the magnitude and time of the negative current exceeds a threshold level, the latch trip signal disabling the high gating of the back-to-back MOSFET associated with the first battery or the second battery. In this embodiment, the comparator circuit can include a high current turn-off threshold and a separate low current turn-off threshold. The high current turn-off threshold can include a shorter duration than the low current turn-off threshold.

[0015] According to other aspects, the present disclosure encompasses a battery pack configured to supply power to a common load and including a first battery and a second battery. A battery protection circuit is configured to detect and prevent negative current from flowing into the first battery and the second battery during a power supply mode of the batteries, thereby preventing uncontrolled charging of the first battery or the second battery due to a voltage difference between the first battery and the second battery.

[0016] In a particular embodiment, the battery protection circuit includes a shunt resistor serially connected between each of the first battery and the second battery and the common load, wherein the battery protection circuit detects negative current flowing through the shunt resistor and isolates the first battery or the second battery when a negative current above a threshold level is detected through the shunt resistor associated with the respective first battery or second battery.

[0017] The battery protection circuit may include a comparator circuit configured to generate a trip signal to isolate the first battery or the second battery when one or a combination of the magnitude and time of the negative current exceeds a threshold level. The comparator circuit may include a high-current turn-off threshold and a separate low-current turn-off threshold.

[0018] The present disclosure also encompasses a method for preventing uncontrolled charging of batteries in a battery pack configured with at least a first battery and a second battery. The method may include configuring back-to-back MOSFETs in series between each of the first battery and the second battery and the common load. With a controller connected to the back-to-back MOSFETs, controlling the gating of the MOSFETs during a power supply mode of the battery pack to prevent the first battery and the second battery from supplying power to the common load in parallel. Accordingly, uncontrolled charging between the first battery and the second battery due to a voltage difference between the first battery and the second battery is prevented.

[0019] The present disclosure encompasses the various methods and functions discussed above and enabled herein.

[0020] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the technology and, together with the description, serve to explain the principles of the technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the description of the drawings, a complete disclosure of the invention for a person of ordinary skill in the art, including the best mode of making and using the system and method, is set forth, in the drawings:

[0022] Figure 1 A portable power tool tethered to a backpack having an internal battery pack is depicted;

[0023] Figure 2A and Figure 2B are diagrams of a conventional battery protection circuit for a single battery in a discharge mode and a charge mode, respectively;

[0024] Figure 3 is a diagram of a multi - battery pack having a battery protection circuit according to aspects of the present invention;

[0025] Figure 4 is a diagram of a circuit having negative current sensing capabilities Figure 3 ;

[0026] Figure 5 is a diagram of a comparator circuit used with a negative current protection circuit; and

[0027] Figure 6 is a diagram of an embodiment of negative current protection. DETAILED DESCRIPTION

[0028] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The word "exemplary" as used herein means "serving as an example, instance, or illustration". Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or superior to other implementations. Further, each example is provided by way of explanation and not limitation of the technology. In fact, it will be apparent to those skilled in the art that modifications and variations can be made to the technology without departing from the scope or spirit of the claimed technology. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Accordingly, this disclosure is intended to cover such modifications and variations that fall within the scope of the appended claims and their equivalents. The detailed description uses numerical and alphabetical labels to refer to features in the drawings. The same or similar labels in the drawings and the description are used to refer to the same or similar parts of the invention.

[0029] As used herein, the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another and are not intended to denote the position or importance of the individual components. Unless the context clearly dictates otherwise, the singular forms "a," "an," and "the" include plural references. Unless otherwise indicated herein, the terms "coupled," "fixed," "attached," etc. refer to both direct coupling, fixing, or attachment, as well as indirect coupling, fixing, or attachment through one or more intermediate components or features. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited to those features, but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not an exclusive or. For example, the condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0030] Approximating terms such as "about," "substantially," "approximately," or "essentially" include values within ten percent greater than or less than the stated value. When used in the context of an angle or direction, such terms include within ten degrees greater than or less than the stated angle or direction. For example, "substantially vertical" includes a direction within ten degrees of vertical in any direction (e.g., clockwise or counterclockwise).

[0031] Advantages, other advantages, and solutions to problems will be described below for specific embodiments. However, advantages, advantages, solutions to problems, and any features that may cause any advantage, advantage, or solution to occur or become more pronounced should not be construed as critical, required, or essential features of any or all of the claims.

[0032] Now referring Figure 1 , a battery pack 10 having a first battery 12, a second battery 14, and a controller 20 is depicted. The battery pack 10 is configured within a backpack 15 that may be worn by a user and is electrically connected to a power tool 18 via an electrical tether 17 to supply power to the tool 18. Figure 1This only depicts known uses of the battery pack 10 and is not intended to be a limitation of the present invention. It should be understood that the battery pack 10 in combination with aspects of the present invention can be configured in any embodiment where multiple batteries are arranged in parallel to deliver power to a load, such as a power tool.

[0033] For ease of explanation only, the batteries 12 and 14 are described herein as lithium-ion batteries. The present disclosure is not limited to the use of lithium-ion batteries.

[0034] Figure 2A and Figure 2B depicts a configuration of a conventional battery protection circuit utilizing a back-to-back MOSFET structure 24 and is discussed herein to provide a background reference for the present disclosure.

[0035] Reference Figure 2A and Figure 2B , the power MOSFET 24 and the driver 26 can be implemented with a solid-state driver (SSD) within the controller 20 or communicate with the controller 20. The MOSFETs are connected in series between the lithium-ion battery 12 and the output load. The controller 20 can be a dedicated IC (integrated circuit) for controlling the gating (i.e., on and off states) of the MOSFET 24 to manage the charging and discharging modes of the battery 12. One of the MOSFETs (Q1) is used to discharge the battery to supply power to the load ( Figure 2A ), and the other MOSFET (Q2) is used to charge the battery ( Figure 2B ). The MOSFET 24 is depicted at the positive electrode (“high side”) of the battery 12. In other embodiments, the MOSFET 24 can be located at the negative electrode (“low side”) of the battery 12. The MOSFET 24 can be a P-channel or N-channel MOSFET, and the drains can be connected in a back-to-back structure, as Figure 2A and Figure 2B depicted.

[0036] In Figure 2A the depicted discharging mode of the battery 12, the IC controller 20 provides a gate drive signal to the driver 26 to drive the discharging MOSFET Q1 to a high (on) state. When Q1 is on, the discharge path (indicated by the arrows in the figure) passes through Q1, across the parasitic diode around Q2, and to the load. In a particular embodiment, the controller 20 can also turn on Q2 (Q2 has a lower resistance than the parasitic diode around Q2) to avoid conduction losses (voltage drop) from the parasitic diode.

[0037] In Figure 2BIn the charging mode of the battery 12 depicted, the IC controller 20 provides a gate drive signal to the driver 26 to drive the charging MOSFET Q2 to the high (conductive) state. When Q2 is conductive, the charging path is through Q2, across the parasitic diode around Q1, and to the battery. In an embodiment, the controller 20 may also turn on Q1 (Q1 has a lower resistance than the parasitic diode around Q1) to avoid conduction losses (voltage drops) from the parasitic diode.

[0038] Figure 3 Illustrated is a battery protection for providing to a plurality of batteries 12, 14 in a battery pack 10 in accordance with an embodiment of the present disclosure. Each of the batteries 12, 14 is provided with a back-to-back MOSFET structure 24 on the high side of the battery as discussed above. The respective gate drivers 26 are controlled by a controller 30, which may be an IC controller.

[0039] Still referring to Figure 3 , if both the discharge MOSFETs Q1-0 and Q1-1 are conductive (gated high) such that the batteries 12, 14 are in a true electrical parallel configuration with respect to a common load 16, and if one or both of the charging MOSFETs Q2-0 or Q2-1 are shorted, and there is a voltage difference between the batteries 12, 14, then an uncontrolled discharge may occur between the batteries 12, 14.

[0040] In Figure 3 , in accordance with aspects of the present disclosure, the controller 30 coordinates the gating signals to the drivers 26 such that the first battery 12 and the second battery 14 do not actually supply power to the common load 16 in parallel. The gating command signals from the controller 30 alternate stepwise such that the states of the discharge MOSFETs Q1-0 and Q1-1 alternate out of sync between the "conductive" and "non-conductive" states, as represented by the gating curves depicted in Figure 3 . Since the batteries 12, 14 do not supply power to the common load 16 in a true parallel (simultaneous) mode, this unique control scheme prevents an uncontrolled discharge from one battery 12 or 14 to the other battery 14 or 12, which may be caused by a voltage difference in the batteries and a failure of one or the other of the charging MOSFETs Q2-0 and Q2-1.

[0041] Figures 4 to 6 Illustrated are additional battery protection features that may be implemented in combination with the embodiments discussed above or as a stand-alone feature in a multi-battery pack.

[0042] Referring to Figure 4, in an uncontrolled discharge between batteries 12, 14, if a path through or around the back-to-back MOSFET structure 24 is established, current will flow in the negative direction into one of the batteries 12, 14. For example, this may occur during a discharge mode when a single point failure occurs in one of the charging MOSFETs Q2-0 / MOSFET Q2-1. The present disclosure proposes detecting this negative current and isolating one or both of the batteries 12, 14 when the detected negative current exceeds a threshold level.

[0043] In Figure 4 an embodiment, the detection device may include a shunt resistor 26 series-connected between the back-to-back MOSFET 24 of each of the first battery 12 and the second battery 14 and a common load 16. The controller 30 measures the negative current flowing through the shunt resistor 26. Referring Figure 5 to, the value of any detected negative current is input to a comparator circuit 36 and compared with two independent thresholds: a low current comparison and a high current comparison. In the low current comparison, a threshold is established for a relatively low negative current value (e.g., greater than 0.5 A) having a relatively long duration (e.g., greater than 1 ms). In the high current comparison, a threshold is established for a relatively high negative current value (e.g., greater than 200 A) having a relatively short duration (e.g., greater than 300 us). When satisfied, these comparator values are sent to a shift register / counter which in turn sends a signal to a multi-channel OR gate structure which generates a signal to a latch circuit 38 when at least one of the comparator events is satisfied for at least one of the battery circuits, as Figure 5 shown.

[0044] Figure 6 depicts an embodiment of the latch function 38. An enable signal is sent to the "latch" driver of a pair of MOSFETs 40 having connected gates, where each MOSFET 40 is connected upstream of the driver 26 of one of the back-to-back MOSFET structures 24. When the MOSFETs 40 are turned on (gated high), they define a ground path for each of the drivers 26, which disables the SSD 25 for each of the batteries 12, 14 and prevents current from flowing into the batteries.

[0045] The present invention also includes various method embodiments for preventing uncontrolled charging of the batteries in a battery pack configured with at least a first battery and a second battery. The method can include configuring back-to-back MOSFETs in series between each of the first battery and the second battery and a common load. With a controller connected to the back-to-back MOSFETs, the gating of the MOSFETs is controlled during the power supply mode of the battery pack to prevent the first battery and the second battery from supplying power to the common load in parallel. Thus, uncontrolled charging between the first battery and the second battery due to the voltage difference between the first battery and the second battery is prevented.

[0046] Another method embodiment that can be combined with the previous method or function as an independent method includes detecting a negative current flowing into each of the first battery and the second battery, and isolating one or both of the first battery and the second battery when the detected negative current flowing into the corresponding first battery or second battery is higher than a threshold level. The method can include detecting a negative current through a shunt resistor placed in series between the back-to-back MOSFETs and the common load.

[0047] This written description uses examples, including the best mode, to disclose the present invention and also enables any person skilled in the art to practice the present invention, including making and using any device or system and performing any combined method. The patentable scope of the present invention is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples include structural elements identical to the literal language of the claims, or if such other examples include equivalent structural elements that do not differ materially from the literal language of the claims, then such other examples are intended to be within the scope of the claims.

Claims

1. A battery pack configured to supply power to a common load, the battery pack comprising: a first battery and a second battery; as well as A battery protection circuit is configured to prevent uncontrolled charging of the first battery or the second battery due to a voltage difference between the first battery and the second battery.

2. The battery pack according to claim 1, wherein: For each of the first battery and the second battery, the battery protection circuit includes a back-to-back MOSFET and a controller, the back-to-back MOSFET being connected in series between the corresponding battery and the common load, and the controller communicating with a gate driver associated with the MOSFET to control gating during a power supply mode of the battery pack to prevent the first battery and the second battery from supplying power in parallel to the common load.

3. The battery pack according to claim 2, wherein: The back-to-back MOSFETs are located at the positive high side of each of the first cell and the second cell.

4. The battery pack according to claim 2, wherein: The battery protection circuit also includes means for detecting a negative current flowing into each of the first battery and the second battery.

5. The battery pack according to claim 4, wherein: The device for detecting includes a shunt resistor connected in series between the back-to-back MOSFETs of each of the first battery and the second battery and the common load, the battery protection circuit detecting a negative current flowing through the shunt resistor and isolating the first battery or the second battery when a negative current above a threshold level is detected through the shunt resistor associated with the corresponding first battery or the second battery.

6. The battery pack according to claim 5, wherein: The battery protection circuit includes a comparator circuit configured to generate a latch trip signal that disables high gating of the back-to-back MOSFETs associated with the first battery or the second battery when one or a combination of the magnitude and time of the negative current exceeds the threshold level.

7. The battery pack according to claim 6, wherein: The comparator circuit includes a high current shutdown threshold and a separate low current shutdown threshold.

8. The battery pack according to claim 7, wherein: The high current shutdown threshold comprises a shorter duration than the low current shutdown threshold.

9. A battery pack configured to supply power to a common load, the battery pack comprising: a first battery and a second battery; as well as A battery protection circuit is configured to detect and prevent negative current from flowing to the first battery and the second battery during a power supply mode of the battery, thereby preventing uncontrolled charging of the first battery or the second battery due to a voltage difference between the first battery and the second battery.

10. The battery pack according to claim 9, wherein: The battery protection circuit includes a shunt resistor connected in series between each of the first battery and the second battery and the common load, the battery protection circuit detects a negative current flowing through the shunt resistor, and isolates the first battery or the second battery when a negative current above a threshold level is detected through the shunt resistor associated with the corresponding first battery or the second battery.

11. The battery pack according to claim 10, wherein: The battery protection circuit includes a comparator circuit configured to generate a trip signal that isolates the first battery or the second battery when one or a combination of a magnitude and a time of the negative current exceeds the threshold level.

12. The battery pack according to claim 11, wherein: The comparator circuit includes a high current shutdown threshold and a separate low current shutdown threshold.

13. A method of preventing uncontrolled charging of a battery in a battery pack, the battery pack being configured with at least a first battery and a second battery, the method comprising: controlling, with a controller connected in series to back-to-back MOSFETs between each of the first battery and the second battery, gating of the back-to-back MOSFETs during a power supply mode of the battery pack to prevent the first battery and the second battery from supplying power in parallel to the common load; and Wherein, uncontrolled charging between the first battery and the second battery due to a voltage difference between the first battery and the second battery is prevented.

14. The method of claim 13, further comprising detecting a negative current flowing into each of the first battery and the second battery. 15 . The method of claim 14 , further comprising isolating the first battery or the second battery upon detecting that the negative current flowing into the corresponding first battery or second battery is above a threshold level.

16. The method according to claim 15, wherein: The negative current is sensed by a shunt resistor placed in series between the back-to-back MOSFETs and the common load.

17. The method according to claim 16, wherein: When the negative current exceeds the threshold level, a trip signal is generated for a latch that disables the high gating of the back-to-back MOSFETs to isolate the first battery or the second battery.

18. The method according to claim 17, wherein: The threshold level is one or a combination of the magnitude and the time of the negative current.

19. The method according to claim 18, wherein: The threshold levels include a high current shutdown threshold and a separate low current shutdown threshold.

20. The method according to claim 19, wherein: The high current shutdown threshold comprises a shorter duration than the low current shutdown threshold.

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